1. Field of the Invention
This invention relates generally to a file for cutting metal, and more particularly to a double angled precision file for sharpening chain saw teeth.
2. Description of the Prior Art
Metal files are currently available in a variety of shapes and with a number of teeth configurations for various metal cutting and shaping applications. Such files are classified according to their shape or cross section and according to their teeth pitch, spacing and cut. The shape or contour may be tapered or it may be uniform about the file's longitudinal axis. The latter shape is defined as blunt. Teeth configurations are designated as single or double cut, rasped or curved. The single cut file has teeth of a uniform size, angle and spacing. The cut depth is relatively shallow and the teeth are closely spaced which produces a smooth finish on the workpiece. Double cut files have two separate sets of teeth, one of which is typically of a coarser cut. Rasp and curved cut files have more deeply cut, wider spaced teeth and are designed for rapid removal of metal. Chain saw files typically are of rectangular, square, round or diamond-shaped sections and may be either double or single cut. The single cut is preferred as these files are used for finishing purposes, although a double cut file may also be employed for finishing purposes. The shape of the file is determined by the type of the chain saw blade to be sharpened; usually a round, hexagonal or triangular cross-section is employed.
Existing files include a cut portion extending approximately three-quarters of the file's length with the remaining uncut portion tapering into a shoulder and handle.
The filing action requires a length of the file to be pushed or drawn across the work. Usually a stroke of several inches is employed for a smooth finish. It is apparent that with existing files having an uncut handle, the handle and the adjacent cut portion will be unused in the filing motion. Because only the file's distal half is used on the work, this half wears out first, rendering the file unusable despite the remaining unworn portions. Even files which are fully cut are not fully utilizable for such precision work. This is because the cut is angled in one direction, and is uniform over the length of the file. The file is thus adapted for filing in one direction only and one cannot simply turn the file around and use the other half because the teeth will be running in the wrong direction. Sharpening chain saw teeth requires a precise stroke to attain the necessary smoothness and sharpness. Additionally, the relative hardness of the chain saw teeth tends to quickly wear a sharpening file.
None of the prior art has solved the problem of non-uniform wear in a precision chain saw sharpening file.